Objective To explore early effectiveness of modified minimally invasive Chevron-Akin (MICA) osteotomy in the treatment of moderate to severe hallux valgus. Methods A clinical data of 49 patients (61 feet) with moderate to severe hallux valgus, who met the selection criteria between December 2019 and October 2022, was retrospectively analyzed. There were 7 males (8 feet) and 42 females (53 feet) with an average age of 38.0 years (range, 15-59 years), including 37 of unilateral foot and 12 of bilateral feet. There were 41 feet of moderate hallux valgus [hallux valgus angle (HVA) 20°-40°] and 10 feet of severe hallux valgus (HVA>40°). All patients underwent modified MICA osteotomy. A transverse osteotomy on the distal end of the first metatarsal bone was performed to replaced the traditional Chevron osteotomy, and three Kirschner wires were used to assist in three-dimensional correction. The other treatments were the same as traditional MICA osteotomy. The HVA, inter metatarsal angle (IMA), Hardy score of the sesamoid, and American Orthopaedic Foot and Ankle Society (AOFAS) score of 61 feet before operation and at last follow-up were recorded, and the results were compared between the various severity of hallux valgus. Results All patients were followed up 6-24 months with an average of 12.0 months. After operation, the redness and swelling around the incision occurred in 1 foot; limited mobility of the metatarsophalangeal joint occurred in 2 feet; mild numbness of the skin occurred in 5 feet; mild inversion of the great toe occurred in 2 feet. No complication such as tendon injury was found. X-ray films showed no abnormal healing, nonunion, or necrosis of the metatarsal head after osteotomy. The healing time of osteotomy ranged from 3 to 4 months, with an average of 3.2 months. At last follow-up, the HVA, IMA, Hardy score of sesamoid, and AOFAS scores all significantly improved when compared with preoperative levels (P<0.05). The AOFAS scores were excellent in 45 feet, good in 15 feet, and fair in 1 foot, with an excellent and good rate of 98.4%. The above indicators for moderate or severe hallux valgus patients were significantly improved when compared with preoperative levels (P<0.05). The changes between pre- and post-operation in HVA, IMA, and Hardy scores of severe hallux valgus were all greater than those of moderate hallux valgus, with significant difference in HVA change between groups (P<0.05), while there was no significant difference in the other two changes (P>0.05). Conclusion Modified MICA osteotomy can achieve good orthopedic effects and early functional improvement in the treatment of moderate to severe hallux valgus.